Control device



May 2, 1961 D. u. HUNTER CONTROL DEVICE Filed July 20, 1956 INVEN'I'OR.

in E JTTORNEYS m 0 w W a W P w I Q a z w r w J v a T J My 3 m z fiw w m.M w? M wlx A 2 m 4. 0M 2% F I m. A an m w actuator 2,982,260CONTROLYDEVICE David U. Hunter, Huntington, N.Y., assignor to FairchildEngine and Airplane Corporation, Bay Shore, N.Y., a corporation ofMaryland Filed July 20, 1956, Ser. No. 599,254 6 Claims. c1. 121-46.

This invention relatesto a control device for'an actuator wherein theoperation of the actuator is adapted to be controlled by apredetermined'relationship of the pressures exerted by two fluids.

The present invention is particularly applicable for controlling theoutput flow of a feed pump for a boiler.

In the operation of a boiler, it is ordinarily desirable to I maintain apredetermined differential between the pressure, of the steam in theboiler and the pressure of the feed water delivered to the boiler. Inaccordance with the present invention, when the pressures of these twofluids reach a predetermined unbalance, an actuator is rendered operableto decrease the speed of operation of the feed pump. If the unbalance isdue to a momentary overspeed of the feed pump, the balance will berestored by the decrease in speed of the pump. If the unbalance,

on the other hand, is due to failure of the pump suction or otherblockage, the speed of the feed pump will decrease and so will afford anopportunity for the pump to be cleared, the suction restored or thedifllculty otherwise remedied.

For a complete understanding of the present invention, reference may bemade to the detailed description of the invention which follows andtothe accompanying drawings wherein:

Fig. 1 is a schematic representation of a boiler system embodying thepresent invention; and i Fig. -2 is an enlarged cross-section viewillustrating the control device of the present invention.

Fig.1 of the drawingsillustrates a typical steam generating systemincluding a boiler 10, a feed pump 11 for supplying water to the boiler,and a prime mover 12, such as a steam t'urbine,'for driving the feedpump. The feed pump, driven by the turbine via the drive'shaft 14, issupplied with feed water from the intake conduit 15a and supplies thefeed water to the boiler through the conduit 15. The turbine, in turn,is driven by steam admitted via the conduit 13. The speed of the turbineis regulated by a throttle valve 16 in the conduit 13, and the throttlevalve is adjusted by a pressure-operated actuator 17 controlled by thecontrol device A of the present invention.

The control device A of the present invention is shown in detail in Fig.2 of the drawings. It comprises generally a hollow cylinder 20, inletports 21, 22 at opposite ends thereof, an intermediate discharge port23, and a slide fvalve 24 having interior passages 25 and 26 therein.The

passage 25 communicates with the inlet port 21, and the passage 26communicates with the inlet port 22. In the cation between the dischargeport 23 and one or the'other of the inlet ports 21 or 22. t a

l The inlet port 21'is connected via a conduit 27 to the conduit 15through which water is fed to the boiler, and the port 22 is connectedvia a conduit 28 to the steam in-the .boiler. Preferably,.-.a cooler 29is interposed in mics v .neutral'position when the pressures exerted bythe fluids at opposite ends of the slide valve are in the desiredrelationship. When, however, the pressures exerted by the fluids atopposite sides of the slide valve are not in the desired relationship,or, stated another way, when the forces at opposite ends of the slidevalve 24 are unbalanced, the slide valve will be shifted axially in onedirection or the other, establishing communication via one of thepassages 25, 26 of the slide valve between one of the inlet ports 21, 22and the discharge port 23.

Stops 33 are provided at both ends of the cylinder 20 to limit themovement ofthe slide valve in the cylinder,

The conduit 28 contains restrictions 34 and 35, and a pressureaccumulator 36 is coupled to the conduit between the restrictions 34 and35. The exhaust port 23 communicates with the valve actuator via aconduit 38, and the conduit 38 contains a restricted vent 39. The sizeof the opening in the vent 39 is greater than the size of the opening ofthe restriction 34, and the size of the opening of the restriction 34downstream of the accumulator, in turn, is greater than the size of theopening of the restriction 35 upstream of the accumulator.

Turning now to a description of the operation of the present, invention,the slide valve is maintained in a neutral position by the pressuresexerted by the fluids in the conduits 27 and 28 and by the compensatingforces exerted by the springs 30, 31 when the fluids acting on the slidevalve are in the proper relationship. In this position of equilibrium,both passages 25 and 26 of the slide valve are closed to the dischargeport 23. Furthermore, in this position of the slide valve, the throttlevalve 16 is open full, and the speed of the turbine controlled byconventional governing means. a

In the event that the water pressure in the conduit 15 increases withoutan equal increase in the steam pressure, the slide valve 24 will beshifted to the right, as viewed in Fig. 2, and water will flow throughthe passage 25 to the conduit 38. When the flow into the conduit 38 isgreater than the discharge through the vent 39, the pressure in theconduit 38 will build up, thereby controlling the operation of theactuator to adjust the valve 16 gradually toward a closed position. Thisthrottling action of the valve 16 slows down the turbine and the feedpump, thereby decreasing the pressure of the feed water in the conduit15. When the pressure has been decreased sufiiciently, the slide valve24 will be restored to neutral position.

In the event that the water pressure in the conduit 15 drops below apredetermined differential in respect to the pressure in line 28, forany reason, such as for example because of a stoppage in the watersupply line 15a or failureof the pump, the steam pressure forces theslide valve 24 to the left, as viewed in Fig. 2, and the steam orcondensate will flow through the passage 26 to the conduit 38. With thevent 39 draining, there will be a substantial pressure drop across therestriction 34, and inasmuch as the restriction 35 is smaller than therestriction 34, the accumulator will drain through the restriction 34.The accumulator, therefore, delivers its reserve energy through therestriction 34, and the pressure in the conduit 38 is increased tooperate the actuator 17 to slow down the prime mover andthe feed pumpduring the time that the accumulator pressure is discharging After theydischarge of the accumulator, the slide a valve 24 will be restoredtoward its neutral position'by l atented Mayz, V

the force of the spring 30, speeding up the turbine and the pump. If inthe meantime the water pressure in the conduit 15 has beenreestablished, equilibrium will be restored. If, on the other hand, thewater pressure has not risen, the slide valve 24 will be again forced tothe left, as viewed in Fig. 2, as soon as the accumulator pressure hasbuilt up again, and the reduced speed cycle repeated as described above.The pressure differential needed to cause reduced speed operation iscontrolled by the rate of the spring 30 and the length of the dead zonebetween ports 26 and 23.

The valve is shown with a very definite underlap or dead space betweenthe passages 25, 26 so that'there is 'a'region of pressure difierentialthroughout which neither fluid is in communication with the actuatorthrough the conduit 38. While the slide valve is in this intermediateposition, the conduit 38 exhausts through the vent 39 and the actuatoropens the valve 16 to speed up the turbine and 'the said pump. Duringnormal operation, the slide valve is in the position shown in Figure 2.That is to say, the passage 25 will be in communication with the conduit38. Thus, when the pump speed decreases and the piston begins to move tothe left, the initial effect is to decrease the effective size of thepassage 25, thereby speeding up the pump. However, as the slide valvecontinues to move to the left, the passage 25 closes and the fluid inthe accumulator is forced through the restriction 34.

There is a pressure drop across the vent 39 as the fluid from theaccumulator is forced through the vent to atmosphere. This pressure dropacross the vent 39 will be less than the pressure drop across therestriction 34. In this connection, it should be borne in mind thatboilers operate at high pressures, usually above 600 p.s.i. There-'fore, the pressure drop across the vent 39 will be high enough toprovide pressure to allow the actuator to close the valve.

The invention has been shown in preferred form only and by way ofexample, and obviously many variations and modifications may be madetherein without departing from the spirit of the invention. Theinvention, therefore, is not to be limited to any specified form orembodiment except in so far as such limitations are set forth in theclaims.

I claim:

1. A control system comprising an actuator, a housing having a chambertherein, a movable pressure-controlled valve within the chamber, saidvalve having a closed position and open positions on either side of saidclosed position, passages communicating with said valve, said passagescommunicating with fluids which act against said valve in oppositedirections, means acting on said valve to -counterbalance thedifferential pressure of the fluids, thereby maintaining the valve in anintermediate position when the fluids are in the desircd'relationship, apassage connecting the valve with the actuator, passage means controlledby said valve establishing communicationbetween one or the other of saidfluids and the actuator when the valve is in either extreme position andcutting oif communication between both fluids and the actuator when thevalve is in an intermediate position, and means to relieve the pressurein the passage connecting the valve with the actuator when the actuatoris cut from. both fluids.

2. A control system as set forth in claim 1 including a pressureaccumulator in at least one of the passages establishing communicationbetween the valve and one of the fluids and characterized in that thepassage upstream of said accumulator is more restricted than saidpassage downstream of said accumulator, permitting the accumulator todischarge into the passage connecting the valve with the actuator whenthe valve is displaced in the appropriate direction.

3. A control system as set forth in "claim 1 including a 4 pressureaccumulator in at least one of the passages establishing communicationbetween the valve and one of the fluids, a restriction in said passageupstream of said accumulator, a restriction in the passage downstream ofsaid accumulator, the opening in the restriction down stream of saidaccumulator being larger than the opening in the restriction upstream ofsaid accumulator, and a restricted vent in the passage communicatingwith the valve and the actuator, the opening in the restricted ventbeing larger than the opening in the restriction downstream of theaccumulator, permitting the accumulator to discharge into the passageconnecting the valve with the actuator when the valve is displaced inthe appropriate direction.

4. A control device comprising an actuator, a chamber therein, a slidevalve movable within the chamber, said slide valve having a closedposition and open positions on either side of said closed position, aninlet port in said chamber for admitting one fluid on one side of theslide valve, another inlet port in said chamber for admitting anotherfluid on the opposite side of the slide valve, a discharge port in saidchamber in communication with the actuator, means acting on the slidevalve to counterbalance the differential pressure exerted by the twofluids on the slide valve, the slide valve being in a closed positionwith no communication between the inlet ports and the discharge portswhen a predetermined relationship is maintained by the pressures of thefluids, but being movable from said closed position when said pressurerelationship is not maintained, thereby establishing communicationbetween the discharge port and one of the inlet ports and controllingthe operation of the actuator, means to relieve the pressure in theactuator when the valve is restored to closed position, and a pressureaccumulator in communication with at least one of said ports whereby theoperation of the actuator is controlled for a duration of time until thepressure in the accumulator is exhausted sufliciently to permit theslide valve to return to closed position.

5. A system for controlling the rate of supply of a liquid comprising apressure responsive actuator operable to decrease the rate of supply ofthe liquid, a housing having a chamber defined therein, a slide valvemovable within the housing chamber, said slide valve having anintermediate closed position and open positions on either side of saidintermediate closed position, an inlet port in said housing at one endof said chamber for admitting a control fluid under pressure to saidhousing chamber on one side of said slide valve, another inlet port insaid housing at the other end of said chamber for admitting a controlfluid under pressure to said housing chamber on the opposite side ofsaid slide valve, one of said control fluids being a liquid, a dischargeport in said housing communicating with said housing chamberintermediate said inlet ports, a pressure transmitting passageconnecting said discharge port with said pressure responsive actuator,means to relieve the pressure in the pressure transmitting passage whenthe valve is restored to intermediate closed position, passage meansconnecting one of said inlet ports with the liquid, and passage meansconnecting the other of said inlet ports with the other of the controlfluids, whereby the slide valve in its intermediate closed positionprevents communication between said discharge port and either of saidinlet ports when a predetermined relationship is maintained between thepressures of the two control fluids, but whereby the slide valve ismovable from said intermediate closed position to a position toestablish communication between said discharge port and one of saidinlet ports when said pressure relationship is not maintained.

6. A system for decreasing the rate of supply ofa liquid in the eventthat the pressure of the liquid increases without a predeterminedincrease in the pressure of another control fluid, and for decreasingthe rate of supply of the liquid for a short interval or for successiveshort intervals in the event that the pressure of the liquid decreaseswithout a predetermined decrease in the pressure of the said othercontrol fluid, said system comprising a pressure responsive actuatoroperable to decrease the rate of supply of the liquid, a housing havinga chamber defined therein, a slide valve movable within the housingchamber, said slide valve having an inter mediate closed position andopen positionson either side of said intermediate closed position, aninlet port in said housing at one end of said chamber for admitting afluid under pressure to said housing chamber on one side of said slidevalve, another inlet port in said housing at the other end of saidchamber for admitting a fluid under pressure to said housing chamber onthe opposite side of said slide valve, a discharge port in saidhousing'communicating with said housing chamber intermediate said inletports, a pressure transmitting passage connecting said discharge portwith said pressure responsive actuator, means to relieve the pressure inthe pressure transmitting passage when the valve is in closed position,passage means connecting one of said inlet ports with said one controlfluid, passage means connecting the other of said inlet ports with thesaid other control fluid, and a pressure accumulator in communicationwith the passage connecting the inlet port with the said other controlfluid, said passage upstream of said accumulator being more ,maintained,the movement of said slide valve in one direction operating saidpressure responsive actuator to produce a decrease in the rate of supplyof the liquid until the predetermined relationship is restored, and themovement of the slide valve in the opposite direction operating saidpressure responsive actuator to produce a decrease in the rate of supplyof the liquid for a time 1 interval determined by the discharge from thepressure restricted than the passage downstream of saidaccumuaccumulator.

References Cited in the file of this patent UNITED STATES PATENTS718,942 Woerner Ian. 20, 1903 868,680 Martin Oct. 22, 1907 1,962,676Albright June 12, 1934 2,354,791 J Boldt Aug. 1, 1944 2,563,374Rosenberger Aug. 7, 1951 r 2,774,369 Di Tirro Dec. 18, 1956 2,889,780-Binford June 9, 1959 FOREIGN PATENTS 354,673 Germany Feb. 26, 1920 GreatBritain June 18, 1948

